1. Field of the Invention
The present invention relates to a connector for an optical fiber in which an optical fiber and an optical conversion element are detachably coupled together or optical fibers are detachably coupled each other, and particularly relates to the construction of a connector which has improved a retaining performance of the optical fiber.
2. Description of the Prior Art
An optical information transmission system using optical fibers and optical conversion elements has been used increasingly. People expect much from optical fibers as one of information transission lines which are less loss yet large capacity.
The optical information transmission system has to use a connector in order to couple the optical fiber to the optical conversion element or couple the optical fibers each other.
One example of a conventional coupling construction in the optical conversion element and optical fibers will be described with reference to FIGS. 8 to 10.
A holding member 1 comprises a front tube portion 1a, a rear tube portion 1b and a flange portion 1c provided therebetween. A plurality of slits 1d are formed in an axial direction in the outer peripheral surface of the rear tube portion 1b, an optical fiber 2 is inserted through the rear tube portion 1 to hold the optical fiber 2 at the front tube portion 1a, and an optical fiber cable 3 coated by a coating portion 3a is held on the rear tube portion 1b. Then, a fixed tube 4 is fitted over the rear tube portion 1b to reduce the diameter of the rear tube portion 1b, and a corner portion 1f formed in the inner peripheral surface of the slit 1d which is in parallel therewith and presses and contacts the outer peripheral surface of the optical fiber cable 3 in the same axial direction to fix the optical fiber cable 3. Further, the front tube portion 1a of the holding member 1 is inserted into a tube portion 6a of an optical receptacle 6 internally provided with an optical conversion element 5, and a cap nut 7 having a projection 7a in the inner periphery thereof is threadedly engaged with the tube portion 6a of the optical receptacle 6 whereby the optical conversion element 5 and the optical fiber 2 may be detachably coupled.
However, the above-described prior art has the following difficulties.
The corner portion 1f of the slit 1d presses and contacts the outer peripheral surface of the optical fiber cable 3 in the same axial direction to fix the optical fiber cable 3. Therefore, the outer peripheral surface of the optical fiber cable 3 and the inner peripheral surface of the rear tube portion 1b are merely in contact with each other in the same axial direction, and after a lapse of time, the optical fiber cable 3 is axially displaced or tends to be slipped out of the holding member 1. Moreover, the fixed tube 4 and the rear tube portion 1b are also merely in the state of surface contact, and when an axial careless force is applied to the fixed tube 4, the fixed tube 4 is often encountered to be slipped out.
For these reasons, the coupling efficiency of the optical fiber and optical conversion element or the mutual optical fibers is deteriorated, thus bringing forth unfavorable results for the optical information transmission system.
There is further shown in FIG. 9 a system in which uneven portions 1e are provided in the inner peripheral surface of the rear tube portion 1b, and the uneven portions 1e are brought into contact with the coating portion 3a to prevent the optical fiber from being slipped out. Also in this case, the sleeve still tends to be slipped out of the holding member 1, and the optical fiber is also possibly displaced in the axial direction. Moreover, since the uneven portions 1e are provided in the inner peripheral surface of the rear tube portion 1b, costs of parts for the holding member 1 increase accordingly, thus not only increasing the cost of products but failing to fully display the function of the connector for the optical fiber.